Method for extracting cellulose, pectin and polyphenol from pear fruit byproducts

Abstract

The invention belongs to the technical field of fruit by-product processing, and particularly relates to a method for extracting cellulose, pectin and polyphenol from pear fruit by-products. According to the method, the thermal mechanochemical effect of steam explosion is utilized to perform steam explosion treatment on the pome byproducts, so that most of hemicelluloses and lignin can be removed, cellulose, pectin and polyphenol can be efficiently and quickly extracted, the production cycle of the cellulose, the pectin and the polyphenol is shortened, and the efficiency is improved; in addition, the combination of choline chloride and ethanol is used as the eutectic solvent, compared with other types of hydrogen bond acceptors and hydrogen bond donors, the polyphenol extraction effect is most remarkable, and the extraction efficiency of the pear fruit byproduct polyphenol can be improved to the maximum extent through a simple process. The method provided by the invention lays a foundation for further development and utilization of pear residue cellulose, pectin and polyphenol, and improves the comprehensive utilization rate of pear fruit processing byproducts.

Description

Technical Field

[0001] The invention belongs to the technical field of fruit by-product processing, and particularly relates to a method for extracting cellulose, pectin and polyphenols from pear fruit by-products. Background Art

[0002] Pear fruit byproducts refer to waste byproducts produced after fresh pears are processed through juicing, drying, canning, etc., mainly including pear skin, pear pulp, pear core and fruit stalk, etc., with a total amount accounting for about 40% to 50% of the original fresh fruit weight. Since pear pomace contains some stone cells, it has poor palatability during rough processing and low recycling rate, so it is usually treated as waste. If fresh pomace is not treated immediately, it is very easy to spoil and mildew, which affects its utilization, causing great troubles to production companies and the environment. However, pear pomace contains a large amount of polysaccharides, phenolic substances, flavonoids, cellulose and hemicellulose, etc., and is a good source of high-quality bioactive components.

[0003] Cellulose is a green and sustainable material that can be used in the manufacture of many high-value products, including regenerated cellulose, cellulose ethers, esters and nanocrystalline cellulose. Cellulose and hemicellulose separation technology has always been a hot topic in the research community. At present, the common methods for extracting cellulose are physical and chemical methods. The former mainly uses high-pressure cooking and microwave treatment, which uses a pretreatment method of crushing the material with sodium hydroxide solution, and then cooking or microwave treatment under high temperature and high pressure. However, the cellulose produced has more impurities and a low extraction rate. Moreover, the high-pressure cooking method often uses large-scale cooking equipment, which consumes a lot of electricity, has excessive pressure, and is dangerous to operate; the chemicals used in the chemical method are prone to secondary pollution to the environment. These methods produce a lot of pollution and cellulose is easily destroyed.

[0004] Pectin is a plant acidic polysaccharide with poly-α-1,4-D-galacturonic acid polysaccharide as the skeleton component. It has good gelling property and emulsification stability and has become an important natural additive in the food industry, medicine, daily chemical and textile industries. At present, the main extraction methods of pectin are acid extraction, enzyme extraction and salt extraction. The most commonly used extraction method is acid extraction, which is usually in an acid solution with a certain pH value, under heating conditions to hydrolyze the original pectin into water-soluble pectin to form a pectin aqueous solution; enzyme extraction is to use cellulase, hemicellulase and other enzymes to remove cellulose, hemicellulose and other substances in the cell wall, enzymatically degrade the macromolecular substances in pectin or convert insoluble pectin into water-soluble pectin, and then extract it. However, the reaction time of enzymatic extraction of pectin is relatively long, usually more than 10 hours; salt extraction usually uses ammonium oxalate to convert insoluble pectin calcium into soluble ammonium salt, thereby increasing the solubility of insoluble pectin. The existing methods generally have the disadvantages of low pectin yield and incomplete extraction.

[0005] Polyphenols, as a major category of secondary metabolites, exist in almost all plants and have potential health-promoting effects. Currently, polyphenol extraction usually uses ethanol for leaching, concentration and purification, and ethyl acetate extraction, as well as acetone for purification of crude products. This method has cumbersome steps, and although the purity of polyphenols is increased, the yield is low. In addition, due to the use of organic solvents such as ethyl acetate and acetone for extraction, there are inevitably reagent residues in the extract, which limits the application of the extract. Summary of the invention

[0006] The purpose of the present invention is to provide a method for extracting cellulose, pectin and polyphenols from pear fruit by-products, thereby improving the extraction rates of cellulose, pectin and polyphenols in pear fruit by-products, and obtaining cellulose with uniform particle size distribution, large aspect ratio and high crystallinity; pectin has the effect of regulating anti-inflammatory activity, and polyphenols have antioxidant activity, thereby improving the utilization rate of pear fruit processing by-products, simplifying the process and protecting the environment.

[0007] In order to achieve the above object, the present invention provides a method for extracting one or more of cellulose, pectin and polyphenols from pear fruit byproducts, comprising the following steps:

[0008] The pear fruit byproduct is subjected to steam explosion treatment and pulverization treatment in sequence to obtain pear residue powder; the steam explosion pressure of the steam explosion treatment is 0.3-2.0 MPa;

[0009] Extracting the pear residue powder; the extraction includes one or more of cellulose extraction, pectin extraction and polyphenol extraction;

[0010] The cellulose extraction step comprises: performing a first extraction on the pear residue powder using an alkaline solution, collecting the filter residue after reduced pressure filtration; bleaching the filter residue using hydrogen peroxide, collecting the filter residue after reduced pressure filtration, and drying to obtain pear crude cellulose; the pH value of the alkaline solution is 8-12.

[0011] The pectin extraction step comprises: performing a second extraction on the pear residue powder using an acid solution and collecting the extract; performing alcohol precipitation on the extract and collecting the precipitate to obtain pear pectin.

[0012] The polyphenol extraction step comprises: mixing the pear residue powder and a low eutectic solvent solution, ultrasonically extracting, and collecting the extract; the extract liquid contains pear fruit polyphenols; the low eutectic solvent solution comprises a hydrogen bond acceptor and a hydrogen bond donor; the hydrogen bond acceptor comprises choline chloride; the hydrogen bond donor comprises ethanol; and the molar ratio of choline chloride to ethanol is 1:(1-3).

[0013] Preferably, the steam explosion treatment time is 1 to 5 minutes; the medium of the steam explosion treatment is saturated water vapor; and the temperature of the saturated water vapor is 160 to 230°C.

[0014] Preferably, the temperature of the first extraction is 75-90°C and the time is 2-4h;

[0015] During the cellulose extraction, the mass volume ratio of the pear residue powder to the alkaline solution is 0.5-2 g:10-50 mL; the alkaline solution includes a sodium hydroxide solution, and the mass concentration of the sodium hydroxide solution is 7.5-15 wt %.

[0016] Preferably, the bleaching treatment is performed 3 times, and each bleaching treatment is performed at a temperature of 75 to 90° C. and for 45 to 70 minutes;

[0017] The mass concentration of the hydrogen peroxide is 1-2.5wt%.

[0018] Preferably, after obtaining the pear fruit crude cellulose, the method further comprises: mixing the pear fruit crude cellulose with a purified solution, reacting at 90 to 120° C. for 20 to 60 minutes, collecting the filter residue after vacuum filtration, and drying to obtain purified pear fruit cellulose;

[0019] The purified solution comprises 70-80wt.% acetic acid solution and 65-70wt.% nitric acid solution; the volume ratio of the acetic acid solution to the nitric acid solution is (1-10):(1-30).

[0020] Preferably, the temperature of the second extraction is 75-85° C. and the time is 1.5-3 h.

[0021] Preferably, during the pectin extraction, the mass volume ratio of the pear residue powder to the acid solution is 0.5-2 g:10-50 mL; the acid solution includes a hydrochloric acid solution, and the concentration of the hydrochloric acid solution is 0.05-0.15 mol / L;

[0022] Preferably, the alcohol precipitation time is 10 to 15 hours; anhydrous ethanol is used for the alcohol precipitation, and the volume ratio of the extract to anhydrous ethanol is 1:(1 to 5).

[0023] Preferably, during the polyphenol extraction, the mass volume ratio of the pear residue powder to the low eutectic solvent solution is 1g:(15-35)mL; and the water content of the mixture of the pear fruit by-product powder and the low eutectic solvent solution is 20-60%.

[0024] Preferably, the ultrasonic extraction time is 20 to 60 minutes and the power is 300 to 700W.

[0025] Beneficial effects:

[0026] The method for extracting one or more of cellulose, pectin and polyphenol from pear fruit by-products provided by the present invention comprises the following steps: steam explosion treatment and crushing treatment are sequentially performed on the pear fruit by-products to obtain pear residue powder; the steam explosion pressure of the steam explosion treatment is 0.3-2.0 MPa; cellulose extraction, pectin extraction or polyphenol extraction is performed on the pear residue powder; the steps of cellulose extraction include: first extraction of the pear residue powder by using an alkaline solution, and collecting the filter residue after decompression and filtration; bleaching the filter residue by using a sodium hypochlorite solution, and collecting the filter residue after decompression and filtration , dried to obtain pear fruit crude cellulose; the pectin extraction step includes: using hydrochloric acid solution to perform a second extraction on the pear residue powder and collecting the extract; performing alcohol precipitation on the extract and collecting the precipitate to obtain pear fruit pectin; mixing the pear residue powder and a low eutectic solvent solution, ultrasonically extracting, and collecting the extract; the extract liquid contains pear fruit polyphenols; the low eutectic solvent solution includes a hydrogen bond acceptor and a hydrogen bond donor; the hydrogen bond acceptor includes choline chloride; the hydrogen bond donor includes ethanol; the molar ratio of choline chloride to ethanol is 1: (1-3). The present invention adopts a steam explosion treatment method and makes full use of the thermomechanical chemical effect of steam explosion, which can effectively remove most of the hemicellulose and lignin in the pear residue powder. Combined with the subsequent extraction steps, cellulose, pectin and polyphenols can be prepared efficiently and quickly, shortening the production cycle of cellulose, pectin and polyphenols, improving efficiency, and laying a foundation for the further development and utilization of pear residue cellulose, pectin and polyphenols. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required to be used in the embodiments are briefly introduced below.

[0028] Figure 1 is the particle size distribution diagram of cellulose under different steam explosion pressures;

[0029] Figure 2 The scanning electron microscope images of cellulose under different steam explosion pressures; different lowercase letters indicate significant data relationships (P<0.05);

[0030] Figure 3 The scanning electron microscope images of cellulose under different steam explosion pressures;

[0031] Figure 4 is the infrared spectra of cellulose under different steam explosion pressures;

[0032] Figure 5 The thermal stability test results of cellulose under different steam explosion pressures are shown in Figure 1, where A is the TGA graph and B is the DTG graph;

[0033] Figure 6The water and oil holding capacity of cellulose under different steam explosion pressures; different lowercase or uppercase letters indicate significant data relationships (P<0.05);

[0034] Figure 7 Figure 2 shows the glucose adsorption capacity (A) and cholesterol adsorption capacity (B) of cellulose under different steam explosion pressures; different lowercase letters indicate significant data relationships (P<0.05);

[0035] Figure 8 The digestibility characteristics of cellulose under different steam explosion pressures;

[0036] Fig. 9 is the pectin extraction rate under different steam explosion pressures; different lowercase letters indicate significant data relationships (P<0.05);

[0037] Fig.10 is the flavonoid and polyphenol content of pectin under different steam explosion pressures; different lowercase letters indicate significant data relationships (P<0.05);

[0038] Fig.11 is the SEM image of pectin under different steam explosion pressures;

[0039] Fig.12 is the FT-IR spectra of pectin at different steam explosion pressures;

[0040] Fig.13 It is the molecular weight elution curve of pectin under different steam explosion pressures;

[0041] Fig.14 This is the effect of different concentrations of pectin on the cell proliferation rate of RAW264.7 cells in comparative example 2;

[0042] Fig.15 is the effect of pectin on TNF-α production in RAW264.7 cells under different steam explosion pressures;

[0043] Fig.16 is the effect of pectin on IL-1β production in RAW264.7 cells under different steam explosion pressures;

[0044] Fig.17 This is a graph showing the extraction results of polyphenols under different deep eutectic solvents (compositions);

[0045] Fig.18 This is a graph showing the extraction results of polyphenols under different deep eutectic solvents (molar ratio of choline chloride and ethanol);

[0046] Fig.19 This is the result diagram of polyphenol extraction at different water contents;

[0047] Fig. 20This is the extraction result diagram of polyphenols under different solid-liquid ratios;

[0048] Fig.21 This is the extraction result diagram of polyphenols under different solid-liquid ratios and the ultrasonic time of polyphenols;

[0049] Fig. 22 is a graph of the in vitro antioxidant capacity of the polyphenol solution obtained in Example 14;

[0050] in, Figures 14 to 22 Different lowercase letters indicate significant data relationship (P<0.05). DETAILED DESCRIPTION

[0051] The present invention provides a method for extracting one or more of cellulose, pectin and polyphenols from pear fruit byproducts, comprising the following steps:

[0052] The pear fruit byproduct is subjected to steam explosion treatment and pulverization treatment in sequence to obtain pear residue powder; the steam explosion pressure of the steam explosion treatment is 0.3-2.0 MPa;

[0053] Extracting the pear residue powder; the extraction includes one or more of cellulose extraction, pectin extraction and polyphenol extraction;

[0054] The cellulose extraction step comprises: performing a first extraction on the pear residue powder using an alkaline solution, collecting the filter residue after reduced pressure filtration; bleaching the filter residue using hydrogen peroxide, collecting the filter residue after reduced pressure filtration, and drying to obtain pear crude cellulose; the pH value of the alkaline solution is 8-12.

[0055] The pectin extraction step comprises: performing a second extraction on the pear residue powder using an acid solution and collecting the extract; performing alcohol precipitation on the extract and collecting the precipitate to obtain pear pectin.

[0056] The polyphenol extraction step comprises: mixing the pear residue powder and a low eutectic solvent solution, ultrasonically extracting, and collecting the extract; the extract liquid contains pear fruit polyphenols; the low eutectic solvent solution comprises a hydrogen bond acceptor and a hydrogen bond donor; the hydrogen bond acceptor comprises choline chloride; the hydrogen bond donor comprises ethanol; and the molar ratio of choline chloride to ethanol is 1:(1-3).

[0057] The present invention performs steam explosion treatment on pear fruit byproducts to obtain pear residue. The steam explosion pressure of the steam explosion treatment of the present invention is 0.3-2.0MPa; as an embodiment, the steam explosion pressure of the steam explosion treatment is 0.3-1.5MPa; as another embodiment, the steam explosion pressure of the steam explosion treatment is 0.3-0.9MPa. As an embodiment, the time of the steam explosion treatment is 1-5min; as another embodiment, the time of the steam explosion treatment is 2-3min. As an embodiment, the medium of the steam explosion treatment is saturated water vapor; as an embodiment, the temperature of the saturated water vapor is 160℃-230℃; as another embodiment, the temperature of the saturated water vapor is 180℃-200℃; as another embodiment, the temperature of the saturated water vapor is 200℃. As an embodiment, the present invention uses a high-pressure tank to perform the steam explosion treatment. The invention adopts a steam explosion treatment mode and fully utilizes the thermomechanical chemical effect of steam explosion, which can effectively remove most of the hemicellulose and lignin in the pear residue powder, and lays a foundation for the efficient and rapid extraction of pear residue cellulose, pectin and polyphenols.

[0058] As an embodiment, the present invention performs a crushing treatment on the pear fruit by-product before performing a steam explosion treatment on the pear fruit by-product. As an embodiment, the crushing treatment time is 2 to 5 minutes; as another embodiment, the crushing treatment time is 2 minutes. As an embodiment, the crushing treatment uses a wall breaking machine.

[0059] After obtaining the pear residue, the present invention performs a crushing treatment on the pear residue to obtain pear residue powder. As one embodiment, the crushing treatment time is 2 to 5 minutes; as another embodiment, the crushing treatment time is 2 minutes. As one embodiment, the crushing treatment uses a wall breaker. As one embodiment, the present invention performs the crushing treatment after drying the pear residue to constant weight. The present invention has no strict requirements on the drying method, and conventional methods in the art can be used.

[0060] After obtaining the pear residue powder, the present invention uses an alkaline solution to perform a first extraction on the pear residue powder, and collects the filter residue after decompression filtration. As an embodiment, the temperature of the first extraction is 75-90°C; as another embodiment, the temperature of the first extraction is 85°C; as an embodiment, the time of the first extraction is 2-4h; as another embodiment, the time of the first extraction is 4h. As an embodiment, the pH value of the alkaline solution is 10. As an embodiment, the mass volume ratio of the pear residue powder and the alkaline solution is 0.5-2g:10-50mL. As an embodiment, the first extraction method is stirring. As another embodiment, the mass volume ratio of the pear residue powder and the alkaline solution is 1g:20mL. As an embodiment, the alkaline solution includes a sodium hydroxide solution, and the mass concentration of the sodium hydroxide solution is 7.5-15wt%; as another embodiment, the mass concentration of the sodium hydroxide solution is 10wt%. The present invention has no strict requirements on the method of decompression filtration, and the conventional method in the art can be used.

[0061] After obtaining the filter residue, the present invention uses hydrogen peroxide to bleach the filter residue, collects the filter residue after vacuum filtration, and dries it to obtain pear fruit crude cellulose. As an embodiment, after obtaining the filter residue, the present invention washes the filter residue to neutrality. As an embodiment, the washing uses distilled water.

[0062] As an embodiment, the bleaching treatment of the present invention is performed three times, and the temperature of each bleaching treatment is 75-90°C; as another embodiment, the temperature of each bleaching treatment is 85°C; as an embodiment, the time of each bleaching treatment is 45-70 minutes; as another embodiment, the time of each bleaching treatment is 60 minutes. As an embodiment, the mass concentration of the hydrogen peroxide is 1-2.5wt%; as another embodiment, the mass concentration of the hydrogen peroxide is 2wt%. As an embodiment, the drying includes freeze drying. The present invention has no strict requirements on the specific steps of the drying, and conventional operations in the art can be used.

[0063] As an embodiment, after obtaining the pear fruit crude cellulose, the present invention mixes the pear fruit crude cellulose and a purified solution, reacts at 90 to 120° C. for 20 to 60 minutes, collects the filter residue after vacuum filtration, and dries to obtain purified pear fruit cellulose. As an embodiment, the purified solution includes 70 to 80 wt.% acetic acid solution and 65 to 70 wt.% nitric acid solution; as another embodiment, the purified solution includes 80 wt.% acetic acid solution and 70 wt.% nitric acid solution. As an embodiment, the volume ratio of the acetic acid solution to the nitric acid solution in the purified solution is (1 to 10): (1 to 30); as another embodiment, the volume ratio of the acetic acid solution to the nitric acid solution in the purified solution is (2 to 8): (10 to 25); as another embodiment, the volume ratio of the acetic acid solution to the nitric acid solution in the purified solution is (5 to 6): (15 to 20). In a specific embodiment, the present invention can arbitrarily select a value within the range of (1 to 10): (1 to 30), such as 1:10, 1:20, 1:25, 1:30, 10:1, 10:2, 10:3, 10:7, 10:10, 10:15, 10:18, 10:20, 10:25 or 10:30, etc. As an embodiment, after obtaining the filter residue, the filter residue is washed neutrally and then subjected to the subsequent drying step. As an embodiment, the washing uses distilled water and 95% v / v ethanol. The present invention has no strict requirements on the method of vacuum filtration, and conventional methods in the art can be used. As an embodiment, the drying includes freeze drying. The present invention has no strict requirements on the specific steps of the drying, and conventional operations in the art can be used.

[0064] The invention adopts a steam explosion treatment mode, fully utilizes the thermomechanical chemical effect of steam explosion, can effectively remove most of the hemicellulose and lignin in the pear residue powder, and after obtaining the pear residue powder, carries out alkali treatment and sodium chlorite bleaching, as well as subsequent purification steps, can efficiently and quickly prepare cellulose, shorten the production cycle of cellulose, improve efficiency, and lay a foundation for the further development and utilization of pear residue cellulose.

[0065] After obtaining the pear residue powder, the present invention uses an acid solution to perform a second extraction on the pear residue powder and collect the extract. As an embodiment, the temperature of the second extraction is 75-85°C; as another embodiment, the temperature of the second extraction is 80°C; as an embodiment, the time of the second extraction is 1.5-3h; as another embodiment, the time of the second extraction is 2h. As an embodiment, the mass volume ratio of the pear residue powder and the acid solution is 0.5-2g:10-50mL. As an embodiment, the second extraction method is stirring. As another embodiment, the mass volume ratio of the pear residue powder and the acid solution is 1g:20mL. As an embodiment, the acid solution includes a hydrochloric acid solution, and the concentration of the hydrochloric acid solution is 0.05-0.15mol / L; as another embodiment, the concentration of the hydrochloric acid solution is 0.1mol / L. As an embodiment, the method of collecting the extract includes cold filtration. The present invention has no strict requirements on the method of cold filtration, and conventional methods in the art can be used.

[0066] After obtaining the extract, the present invention performs alcohol precipitation on the extract, collects the precipitate, and obtains pear pectin. As an embodiment, the alcohol precipitation time is 10 to 15 hours; as another embodiment, the alcohol precipitation time is 12 hours. As an embodiment, the alcohol precipitation uses anhydrous ethanol, and the volume ratio of the extract to anhydrous ethanol is 1: (1 to 5); as another embodiment, the volume ratio of the extract to anhydrous ethanol is 1: 3.

[0067] The invention adopts a steam explosion treatment mode, fully utilizes the thermomechanical chemical effect of steam explosion, can effectively remove most of the hemicellulose and lignin in the pear residue powder, after the pear residue powder is obtained, acid solution extraction and alcohol precipitation are performed, pectin can be prepared efficiently and quickly, the production cycle of pectin is shortened, the efficiency is improved, and the foundation is laid for the further development and utilization of pear residue pectin.

[0068] After obtaining the pear residue powder, the present invention mixes the pear residue powder and a low eutectic solvent solution, performs ultrasonic extraction, and collects the extract; the extract liquid contains pear fruit polyphenols; the low eutectic solvent solution includes a hydrogen bond acceptor and a hydrogen bond donor; the hydrogen bond acceptor includes choline chloride; the hydrogen bond donor includes ethanol; the molar ratio of choline chloride to ethanol is 1:(1-3); as another embodiment, the molar ratio of choline chloride to ethanol is 1:2. As an embodiment, the mass volume ratio of the powder of the pear fruit by-product of the present invention to the low eutectic solvent solution is 1g:(15-35)mL; as another embodiment, the mass volume ratio of the powder of the pear fruit by-product to the low eutectic solvent solution is 1g:(20-30)mL. As an embodiment, the water content of the mixture of the powder of the pear fruit by-product and the low eutectic solvent solution is 20-60%; as another embodiment, the water content of the mixture of the powder of the pear fruit by-product and the low eutectic solvent solution is 30-50%; as another embodiment, the water content of the mixture of the powder of the pear fruit by-product and the low eutectic solvent solution is 40%. As an embodiment, the time of the ultrasonic extraction is 20-60 minutes; as another embodiment, the time of the ultrasonic extraction is 20 or 40 minutes. As an embodiment, the power of the ultrasonic extraction is 300-700W; as another embodiment, the power of the ultrasonic extraction is 360W.

[0069] The present invention uses a combination of choline chloride and ethanol as a low eutectic solvent, which has the characteristics of low melting point and low toxicity, can protect the environment, and has the most significant polyphenol extraction effect compared with other types of hydrogen bond acceptors and hydrogen bond donors. Through a simple process, the extraction efficiency of polyphenols, a by-product of pear fruit, can be maximized.

[0070] To further illustrate the present invention, the method for extracting cellulose, pectin and polyphenols from pear fruit by-products provided by the present invention is described in detail below in conjunction with the accompanying drawings and examples, but they should not be construed as limiting the scope of protection of the present invention.

[0071] Example 1

[0072] A method for extracting cellulose from pear byproducts, comprising the following steps:

[0073] (1) Pretreatment: The pear byproducts were crushed with a wall-breaking machine for 2 min to obtain pear residue;

[0074] (2) Steam explosion: put the pear residue into the high-pressure tank of the steam explosion test bench, use saturated water vapor as the medium, the temperature of the saturated water vapor is 180°C to 230°C, the steam explosion pressure is 0.3 MPa, the pressure maintenance time is 3 min, quickly open the high-temperature and high-pressure valve to release the material into the storage tank, collect the pear residue in the storage tank, dry it to constant weight, and then use a wall breaking machine to crush the dried pear residue for 2 min to obtain pear residue powder for later use;

[0075] (3) Crude extraction of cellulose: 50 g of pear residue powder was placed in 1000 mL of 10 wt% sodium hydroxide solution, and then stirred in a water bath at 85°C for 4 h. After stirring, the residue was filtered under reduced pressure and washed to neutrality; the residue was bleached three times with 1000 mL of 2 wt% sodium hypochlorite solution and then filtered under reduced pressure; the residue after reduced pressure filtration was thoroughly washed with distilled water to neutrality, and freeze-dried to obtain crude cellulose;

[0076] (4) Purification of cellulose: 10 g of crude cellulose was placed in 300 mL of a mixed solution of 80 wt% acetic acid and 70 wt% nitric acid (the volume ratio of 80 wt% acetic acid and 70 wt% nitric acid was 10:1) and reacted at 100°C for 30 min. After the reaction was completed, the filtrate was filtered under reduced pressure, and the residue was thoroughly washed with distilled water until it was neutral and then freeze-dried to obtain pure cellulose.

[0077] Example 2

[0078] A method for extracting cellulose from pear by-products is similar to Example 1, the only difference being that during the steam explosion in step (2), the explosion pressure is 0.6 MPa.

[0079] Example 3

[0080] A method for extracting cellulose from pear fruit by-products is similar to Example 1, the only difference being that during the steam explosion in step (2), the explosion pressure is 0.9 MPa.

[0081] Comparative Example 1

[0082] A method for extracting cellulose from pear fruit by-products is similar to Example 1, the only difference being that during the steam explosion in step (2), the explosion pressure is 0.1 MPa at normal pressure.

[0083] Test Example 1 Determination of cellulose extraction rate

[0084] According to the content of the obtained pear residue cellulose, the extraction rates of crude cellulose and pure cellulose in Examples 1 to 3 and Comparative Example 1 were statistically analyzed, and the results are shown in Table 1.

[0085] Table 1 Extraction rates of crude cellulose and pure cellulose under different treatment methods

[0086] Processing Steam explosion pressure / MPa Crude cellulose extraction rate Pure cellulose extraction rate Comparative Example 1 0.1 <![CDATA[22.28±0.04 c ]]> <![CDATA[12.07±0.39 c ]]> Example 1 0.3 <![CDATA[28.38±0.68 b ]]> <![CDATA[17.26±1.33 b ]]> Example 2 0.6 <![CDATA[32.18±1.02 a ]]> <![CDATA[18.90±0.52 b ]]> Example 3 0.9 <![CDATA[34.07±0.43 a ]]> <![CDATA[24.03±1.15 a ]]>

[0087] Note: Different lowercase letters in the same column in the table represent significant data relationship (P<0.05), the same below.

[0088] According to Table 1, compared with the pear residue without steam explosion treatment (Comparative Example 1), the extraction rate of cellulose from the pear residue after steam explosion treatment increased significantly. Moreover, the extraction rates of crude cellulose and pure cellulose increased with the increase of steam explosion pressure. During steam explosion, acidic hydrolysis, mechanical fracture, hydrogen bond destruction, and structural rearrangement occurred, which increased the extraction rate of cellulose from the pear residue.

[0089] Test Example 2 Determination of Cellulose Structure Characterization

[0090] The pure cellulose obtained in Examples 1 to 3 and Comparative Example 1 was used as the test sample and the following test was performed.

[0091] (1) The particle size of the sample to be tested was measured using a Malvern particle size analyzer. The results showed that, compared with Comparative Example 1, the steam explosion treatment of Examples 1 to 3 could reduce the particle size of cellulose. As the steam explosion pressure increased, the particle size first decreased and then increased ( Figure 1 ). During steam explosion, acidic hydrolysis occurs, causing low molecular weight substances to dissolve and the fiber polymerization degree to decrease; mechanical fracture occurs, causing the macromolecular bonds to break and the amorphous region to be destroyed; structural rearrangement occurs, increasing the mobility of the cellulose chain, which is conducive to the change of cellulose to an ordered structure.

[0092] (2) The Zeta potential of the sample to be tested was characterized by a Zeta potential meter. The results showed that the Zeta potential result was opposite to the particle size distribution result. Compared with Comparative Example 1, steam explosion treatment of Examples 1 to 3 could increase the Zeta potential of cellulose. The Zeta potential was negatively correlated with the particle size ( Figure 2 ). In addition, the cellulose obtained in Comparative Example 1 and Examples 1 to 3 all have negative charges, indicating that when the cellulose is purified using acid, uronic acid groups are generated, so it has negative charges.

[0093] (3) The morphology of the samples was characterized by scanning electron microscopy. The results showed that the cellulose particles of Example 1 without steam explosion were larger and smoother; the particle sizes of Examples 1 to 3 were reduced after steam explosion and were mostly porous ( Figure 3 ), which is due to the removal of lignin and hemicellulose, the damage to the dense fiber structure, and the degradation of cellulose caused by steam explosion.

[0094] (4) The molecular structure of the samples was characterized by infrared spectroscopy. The results showed that different samples had a -1 and 2800cm -1There are two relatively strong absorption peaks between them, which are the characteristic peaks of stretching vibration of -OH and -CH. These two groups exist in all three components. -1 The absorption peak corresponds to the characteristic peaks of the acetyl and sugar carbonyl groups of hemicellulose, or the characteristic peaks of the carboxylic acid ester groups of ferulic acid and p-coumaric acid in lignin. The peak appears slightly weakened, indicating partial hydrolysis of hemicellulose or lignin ( Figure 4 ). Because the experimental temperature of 200°C is within the temperature range where hemicellulose is most susceptible to hydrolysis, it indicates that hemicellulose has been hydrolyzed during the steam explosion pretreatment, resulting in a weakening of the absorption peak intensity at this location.

[0095] (5) The weight loss between 20 and 130°C is due to the absorption of water by the material, including semi-absorbed water and intermolecular hydrogen bonds. The weight loss between 240 and 400°C is due to the loss of hemicellulose and cellulose. The thermal stability of the samples was characterized by thermogravimetric analysis. The results showed that the weight loss of the cellulose in Example 1 that was not subjected to steam explosion treatment continued to increase ( Figure 5 The characteristic peak temperatures of thermal decomposition of cellulose obtained at different steam explosion pressures (0.1MPa, 0.3MPa, 0.6MPa and 0.9MPa) are 282.25℃, 302.28℃, 296.73℃ and 322.75℃, respectively. This indicates that the cellulose extracted after steam explosion in Examples 1 to 3 has a high thermal stability ( Figure 5 (B).

[0096] Test Example 3 Determination of Cellulose Functional Properties

[0097] The pure cellulose obtained in Examples 1 to 3 and Comparative Example 1 was used as the test sample and the following test was performed.

[0098] (1) The water holding capacity and oil holding capacity of the samples to be tested were measured by weighing method. The results showed that the steam explosion treatment of Examples 1 to 3 could significantly enhance the water holding capacity and oil holding capacity of cellulose. Both the water holding capacity and oil holding capacity increased first and then decreased with the steam explosion pressure. Figure 6 ). It is related to the particle size. The smaller the particle size, the larger the contact area and the stronger the ability to absorb water and oil.

[0099] (2) The DNS colorimetric method was used to determine the glucose adsorption of the sample, and the o-phthalaldehyde method was used to determine the cholesterol adsorption. The results showed that the glucose adsorption and cholesterol adsorption increased first and then decreased with the increase of steam explosion pressure. Steam explosion treatment can improve the adsorption characteristics of cellulose ( Figure 7 ). Steam explosion treatment can reduce the particle size, increase the area of ​​glucose and cholesterol contacting cellulose, and thus improve the adsorption characteristics.

[0100] (3) The digestion characteristics of the samples to be tested were simulated by using the in vitro gastrointestinal tract, where 0 to 4 hours were simulated digestion in the stomach and 4 to 8 hours were simulated digestion in the intestine. The results showed that cellulose was mainly digested in the stomach. The digestibility increased with the increase of steam explosion pressure, and steam explosion improved the digestion of cellulose ( Figure 8 ), which is related to the particle size.

[0101] Example 4

[0102] A method for extracting pectin from pear fruit byproducts comprises the following steps:

[0103] (1) Pretreatment: The pear byproducts were crushed with a wall-breaking machine for 2 min to obtain pear residue;

[0104] (2) Steam explosion: put the pear residue into the high-pressure tank of the steam explosion test bench, use saturated water vapor as the medium, the temperature of the saturated water vapor is 180°C to 230°C, the steam explosion pressure is 0.3 MPa, the pressure maintenance time is 3 min, quickly open the high-temperature and high-pressure valve to release the material into the storage tank, collect the pear residue in the storage tank, dry it to constant weight, and then use a wall breaking machine to crush the dried pear residue for 2 min to obtain pear residue powder for later use;

[0105] (3) Extraction of pectin: The pear residue powder obtained in step (2) was placed in a 0.1 mol / L HCl solution, stirred at 80°C for 2 h, cooled and filtered, and the filtrate was collected; the filtrate was then precipitated with 3 times the volume of anhydrous ethanol for 12 h, the precipitate was collected by filtration, and dried at 50°C to constant weight to obtain pectin.

[0106] Example 5

[0107] A method for extracting pectin from pear fruit by-products is similar to Example 4, the only difference being that during the steam explosion in step (2), the explosion pressure is 0.6 MPa.

[0108] Example 6

[0109] A method for extracting pectin from pear fruit by-products is similar to Example 4, the only difference being that during the steam explosion in step (2), the explosion pressure is 0.9 MPa.

[0110] Example 7

[0111] A method for extracting pectin from pear fruit by-products is similar to Example 4, the only difference being that during the steam explosion in step (2), the explosion pressure is 1.2 MPa.

[0112] Example 8

[0113] A method for extracting pectin from pear fruit by-products is similar to Example 4, the only difference being that during the steam explosion in step (2), the explosion pressure is 1.5 MPa.

[0114] Comparative Example 2

[0115] A method for extracting pectin from pear fruit by-products is similar to Example 4, the only difference being that during the steam explosion in step (2), the explosion pressure is 0.1 MPa at normal pressure.

[0116] Test Example 4

[0117] The pectins obtained in Examples 4 to 8 and Comparative Example 2 were used as test samples and the following tests were performed.

[0118] (1) The pectin extraction rates of Examples 4 to 8 and Comparative Example 2 were statistically analyzed. The results showed that, compared with Comparative Example 2 (0.1 MPa), the extraction rate showed a trend of first increasing and then decreasing with the increase of steam explosion pressure. The maximum value appeared at 0.3 MPa, with an extraction rate of 8.76%, and the minimum value appeared at 1.5 MPa, which was 3.51% ( Fig. 9 ). This may be because the cellulose polymerization degree of the cell structure decreases under high temperature and high pressure steam, the hemicellulose is partially degraded, the lignin softens, and the lateral connection strength of the cell decreases. When the pressure is suddenly reduced, the steam in the pores of the apple pomace expands rapidly, the "explosion" effect produced by the rapid expansion peels off the lignin, and tears the pear pomace cell tissue into fine fibers, allowing the extraction solvent to fully penetrate, which is conducive to the alcohol precipitation of pectin. However, when the pressure is high, carbonization is prone to occur, so the yield is reduced. Therefore, the optimal steam explosion pressure is 0.3MPa.

[0119] (2) The total phenol content of the sample was determined by the Folin-Ciocalteu method, and the total flavonoid content of the sample was determined by the nitrite-aluminum nitrate-sodium hydroxide colorimetric method. The results showed that with the continuous increase of steam explosion pressure, the total flavonoid content and total phenol content continued to increase, reaching the maximum at 1.5 MPa, which were 42.203 mg / mL and 1.316 mg / g, respectively, which were 45.04 times and 5.62 times higher than those of the total flavonoid content of 0.937 mg / mL and total phenol content of 0.234 mg / g in Comparative Example 2 (0.1 MPa), respectively. Fig.10 ). It is speculated that this is because the higher the saturated steam pressure, the greater the mechanical action, the more serious damage to the intact structure of the bioactive substance, the smaller the mass transfer resistance, and the more conducive to the extraction of bioactive substances.

[0120] (3) The samples were scanned using a Zeiss Sigma 300 scanning electron microscope. The results showed that the surface of the pectin in Comparative Example 2 that was not treated with steam explosion showed a loose and porous state compared to the entangled state of the pectin after treatment with 1.2 MPa and 1.5 MPa. As the steam explosion pressure increased, 0.3 MPa and 0.6 MPa showed a more dense and porous state ( Fig.11), which may be caused by structural damage due to the increase of gas explosion pressure. As the gas explosion pressure continues to increase, the surface tends to be flat, the wrinkles increase, and they are all flaky, and the degree of fragmentation and irregularity of pectin are different. This may be caused by the different chemical composition, linear structure and branched structure of pectin.

[0121] (4) The infrared spectra of the samples were measured by potassium bromide tablet method. The results showed that the infrared spectra of the samples were all at 3364 cm -1 The broad peaks are due to the stretching vibration of OH within or between molecules; both are at 1735 cm -1 There is an absorption peak near 1629 cm -1 There are strong absorption peaks near 1014 cm -1 The absorption peak near is caused by the stretching vibration of CO. The pectins obtained in Examples 4 to 8 and Comparative Example 2 have the same type of structural regions, in the "fingerprint region" (1300-800 cm -1 ) range indicates that pectins differ slightly in structure and monosaccharide composition ( Fig.12 ).

[0122] (5) The molecular weight of the sample was determined by GPC gel permeation chromatography. The results are shown in Table 2 and Fig.13 .

[0123] Table 2 Weight average molecular weight, number average molecular weight and polydispersity coefficient of different pectin samples

[0124] Pectin samples Steam explosion pressure / MPa <![CDATA[Weight-average molecular weight (M w )]]> <![CDATA[Number average molecular weight (M n )]]> <![CDATA[Polydispersity index (M w / M n )]]> Comparative Example 2 0.1 509132 359374 1.47 Example 4 0.3 679979 477961 1.42 Example 5 0.6 352856 306712 1.15 Example 6 0.9 483850 292675 1.65 Example 7 1.2 446816 343677 1.3

[0125] According to Table 2 and Fig.13 It can be seen that the molecular weight distribution of different pectin samples is uneven, showing a wide distribution phenomenon. Mainly composed of three peaks, the molecular weight of the pectin of the present invention is mainly concentrated in the range of 352-679kDa. They respectively account for 36.81% (1.2MPa) to 91.46% (0.9MPa) of the total number of molecules, and also contain some small molecule peaks in the range of 1.3 to 167kDa, accounting for 1.51% (0.9MPa) to 37.97% (1.2MPa) of the total number of molecules. It is speculated that some small molecule proteins, soluble pigments and inorganic salts remaining in the process of extracting polysaccharides may be more concentrated than comparative example 2. The molecular weight distribution of pectin obtained in Examples 4 to 8 is more concentrated.

[0126] (6) Liquid chromatography was performed using Shimadzu LC-2030C 3D PLUS system to determine the monosaccharide composition and pectin structure of the sample. The results are shown in Tables 3 and 4.

[0127] Table 3 Monosaccharide composition of different pectin samples (molar percentage, %)

[0128]

[0129] Table 4 Structural information of different pectin samples

[0130]

[0131] According to Tables 3 and 4, different pectin samples are all typical RG-I type pectin, in which the main monosaccharide species include glucose, fructose, arabinose, rhamnose, galacturonic acid, mannose, galactose and xylose, among which the GalA molar ratio is the highest at 0.6MPa, reaching 28.98%, and the lowest is 10.83% at 1.2MPa, the Ara molar percentage is the highest at 30.10% (0.9MPa), and the lowest is 6.94% (1.2MPa), and the Rha molar percentage ranges from 4.58% (1.2MPa) to 9.86% (0.6MPa). It is generally believed that pectin is mainly composed of HG and RG-Ⅰ regions, the HG region is mainly composed of galacturonic acid, and the main chain of the RG-Ⅰ region is composed of rhamnose and galactose. Therefore, the Rha / GalA ratio can be used to reflect the amount of RG-Ⅰ region structure in pectin. The closer the ratio is to 1, the greater the proportion of RG-Ⅰ region structure in pectin. The (Ara+Gal) / Rha ratio reflects the degree of branching in the RG-Ⅰ region. The proportion of HG region in pectin ranges from 2.52% (1.5MPa) to 19.12% (0.6MPa), while the proportion of RG-I region ranges from 26.94% (1.2MPa) to 67.34% (0.6MPa), which has typical RG-I type pectin characteristics. The results of branching degree show that pear pectins treated in various ways have good branching degrees. Compared with Comparative Example 2, the pectins obtained in Examples 4 to 8 have fewer straight chains and more branches.

[0132] (7) An in vitro cell experiment (Zhu Junhao. Structural characterization of extracellular polysaccharides of Sichuan Ganoderma lucidum and its immunomodulatory effect [D]. Chengdu University, 2021.) was used, with blank culture medium as blank control (BC) and lipopolysaccharide as positive control (LPS) to determine the effects of different concentrations of pectin (2, 4, 6, 8, 10 mg / mL) in Comparative Example 2 on the activity of RAW264.7 cells. The results showed that the pectin obtained in Comparative Example 2 could increase the proliferation rate of RAW264.7 cells without toxic side effects ( Fig.14). After determining that the optimal pectin concentration is 8 mg / mL, the effect of the pectin obtained in Comparative Example 2 and Examples 4 to 7 on the anti-inflammatory activity of RAW264.7 cells was determined. The results showed that the secretion of TNF-α of RAW264.7 cells treated with pectin was significantly reduced compared with the LPS model group, and the secretion of TNF-α of the pectin obtained in Examples 4 to 7 was more significantly reduced than that in Comparative Example 2. The pectin obtained in the present invention has certain anti-inflammatory activity ( Fig.15 ); Compared with the blank control (BC), the secretion of IL-1β increased significantly after LPS induction, and the secretion of IL-1β in each group after pectin treatment was significantly reduced compared with the LPS model group. Among them, the 0.9MPa pectin treatment group had the lowest IL-1β secretion, which was 16.44pg / mL, and the anti-inflammatory effect was better ( Fig.16 ).

[0133] Example 9

[0134] A method for extracting polyphenols from pear fruit byproducts, comprising the following steps:

[0135] (1) Pretreatment: The pear byproducts were crushed with a wall-breaking machine for 2 min to obtain pear residue;

[0136] (2) Steam explosion: put the pear residue into the high-pressure tank of the steam explosion test bench, use saturated water vapor as the medium, the temperature of the saturated water vapor is 180°C to 230°C, the steam explosion pressure is 0.6 MPa, the pressure maintenance time is 2 min, quickly open the high-temperature and high-pressure valve to release the material into the storage tank, collect the pear residue in the storage tank, dry it to constant weight, and then use a wall breaking machine to crush the dried pear residue for 2 min to obtain pear residue powder for later use;

[0137] (3) Extraction of polyphenols: Accurately weigh 0.2 g of the pear residue powder obtained in step (2), add a corresponding volume of a low eutectic solvent to the pear residue powder according to a solid-liquid ratio of 1 g:20 mL, control the water content to 30%, perform 360 W ultrasonic extraction at room temperature for 40 min, centrifuge at 7500 r / min for 10 min, take the supernatant, obtain a polyphenol solution, and store it for later use;

[0138] The low eutectic solvent is any one of Chcl-CA solution, Chcl-MA solution, Chcl-Fru solution, Chcl-Xyl solution, Chcl-EA solution and Chel-EtOH solution;

[0139] The Chcl-CA solution is composed of citric acid and choline chloride, wherein the molar ratio of citric acid to choline chloride is 2:1;

[0140] The Chcl-MA solution is composed of malic acid and choline chloride, wherein the molar ratio of malic acid to choline chloride is 2:1;

[0141] The Chcl-Fru solution is composed of galactose and choline chloride, wherein the molar ratio of galactose to choline chloride is 2:1;

[0142] The Chcl-Xyl solution is composed of xylose and choline chloride, wherein the molar ratio of xylose to choline chloride is 2:1;

[0143] The Chcl-EA solution is composed of choline chloride and ethyl acetate, wherein the molar ratio of choline chloride to ethyl acetate is 1:2;

[0144] The Chcl-EtOH solution consists of choline chloride and ethanol, wherein the molar ratio of choline chloride to ethanol is 1:2.

[0145] Test Example 5

[0146] The concentration of polyphenols in the polyphenol solutions extracted with different deep eutectic solvents in Example 9 was determined by Folin-phenol colorimetry. The results showed that the combined extraction rate of ethanol and choline chloride was the highest, reaching 5.53%, which was significantly higher than that of other deep eutectic solvents ( Fig.17 ).

[0147] Example 10

[0148] A method for extracting polyphenols from pear fruit byproducts, comprising the following steps:

[0149] (1) Pretreatment: The pear byproducts were crushed with a wall-breaking machine for 2 min to obtain pear residue;

[0150] (2) Steam explosion: put the pear residue into the high-pressure tank of the steam explosion test bench, use saturated water vapor as the medium, the temperature of the saturated water vapor is 180°C to 230°C, the steam explosion pressure is 0.6 MPa, the pressure maintenance time is 2 min, quickly open the high-temperature and high-pressure valve to release the material into the storage tank, collect the pear residue in the storage tank, dry it to constant weight, and then use a wall breaking machine to crush the dried pear residue for 2 min to obtain pear residue powder for later use;

[0151] (3) Extraction of polyphenols: Accurately weigh 0.2 g of the pear residue powder obtained in step (2), and add a corresponding volume of a low eutectic solvent composed of choline chloride and ethanol (the molar ratio of choline chloride to ethanol is (3:1, 2:1, 1:1, 1:2 or 1:3) to the pear residue powder according to a solid-liquid ratio of 1 g:20 mL, and control the moisture content to 30%. Perform 360 W ultrasonic extraction at room temperature for 40 min, centrifuge at 7500 r / min for 10 min, take the supernatant, and obtain a polyphenol solution, which is stored for later use.

[0152] Test Example 6

[0153] The concentration of polyphenols in the polyphenol solutions extracted with different deep eutectic solvents in Example 10 was determined by Folin phenol colorimetry. The results showed that the polyphenol extraction rate increased with the increase of the molar percentage of ethanol in the system, reaching a maximum of 5.32% at 1:2, which was significantly higher than that of other treatments ( Fig.18 ).

[0154] Embodiment 11

[0155] (1) Pretreatment: The pear byproducts were crushed with a wall-breaking machine for 2 min to obtain pear residue;

[0156] (2) Steam explosion: put the pear residue into the high-pressure tank of the steam explosion test bench, use saturated water vapor as the medium, the temperature of the saturated water vapor is 180°C to 230°C, the steam explosion pressure is 0.6 MPa, the pressure maintenance time is 2 min, quickly open the high-temperature and high-pressure valve to release the material into the storage tank, collect the pear residue in the storage tank, dry it to constant weight, and then use a wall breaking machine to crush the dried pear residue for 2 min to obtain pear residue powder for later use;

[0157] (3) Extraction of polyphenols: Accurately weigh 0.2 g of the pear residue powder obtained in step (2), add a low eutectic solvent consisting of choline chloride and ethanol (molar ratio of choline chloride to ethanol is 1:2) to the pear residue powder at a solid-liquid ratio of 1 g:20 mL, control the moisture content to 10%, 20%, 30%, 40%, 50% or 60%, perform 360 W ultrasonic extraction at room temperature for 40 min, centrifuge at 7500 r / min for 10 min, take the supernatant, obtain a polyphenol solution, and store it for later use.

[0158] Test Example 7

[0159] The concentration of polyphenols in different polyphenol solutions in Example 11 was determined by Folin phenol colorimetry. The results showed that the polyphenol extraction rate first increased and then decreased with the increase of the water content of the system. The extraction rate was the highest at 50% water content, which was 0.16%, significantly higher than that of other treatments ( Fig.19 ).

[0160] Example 12

[0161] A method for extracting polyphenols from pear fruit byproducts, comprising the following steps:

[0162] (1) Pretreatment: The pear byproducts were crushed with a wall-breaking machine for 2 min to obtain pear residue;

[0163] (2) Steam explosion: put the pear residue into the high-pressure tank of the steam explosion test bench, use saturated water vapor as the medium, the temperature of the saturated water vapor is 180°C to 230°C, the steam explosion pressure is 0.6 MPa, the pressure maintenance time is 2 min, quickly open the high-temperature and high-pressure valve to release the material into the storage tank, collect the pear residue in the storage tank, dry it to constant weight, and then use a wall breaking machine to crush the dried pear residue for 2 min to obtain pear residue powder for later use;

[0164] (3) Extraction of polyphenols: Accurately weigh 0.2 g of the pear residue powder obtained in step (2), and add a low eutectic solvent composed of choline chloride and ethanol (molar ratio of choline chloride to ethanol is 1:2) to the pear residue powder according to different solid-liquid ratios (1:10, 1:15, 1:20, 1:25, 1:30, 1:35, unit: g:mL), control the moisture content to 50%, perform 360W ultrasonic extraction at room temperature for 40 min, centrifuge at 7500 r / min for 10 min, take the supernatant, and obtain a polyphenol solution, which is stored for later use.

[0165] Test Case 8

[0166] The concentration of polyphenols in different polyphenol solutions in Example 12 was determined by Folin phenol colorimetry. The results showed that the polyphenol extraction rate first increased and then decreased with the decrease of the solid-liquid ratio of the system. The extraction rate ranged from 0.91% (1:10) to 2.76% (1:30). The extraction rate was the highest at a solid-liquid ratio of 1:30, which was 2.76%, significantly higher than that of other treatments ( Fig. 20 ).

[0167] Example 13

[0168] A method for extracting polyphenols from pear fruit byproducts, comprising the following steps:

[0169] (1) Pretreatment: The pear byproducts were crushed with a wall-breaking machine for 2 min to obtain pear residue;

[0170] (2) Steam explosion: put the pear residue into the high-pressure tank of the steam explosion test bench, use saturated water vapor as the medium, the temperature of the saturated water vapor is 180°C to 230°C, the steam explosion pressure is 0.6 MPa, the pressure maintenance time is 2 min, quickly open the high-temperature and high-pressure valve to release the material into the storage tank, collect the pear residue in the storage tank, dry it to constant weight, and then use a wall breaking machine to crush the dried pear residue for 2 min to obtain pear residue powder for later use;

[0171] (3) Extraction of polyphenols: Accurately weigh 0.2 g of the pear residue powder obtained in step (2), add a low eutectic solvent consisting of choline chloride and ethanol (choline chloride: ethanol molar ratio of 1:2) to the pear residue powder according to a solid-liquid ratio of 1 g:30 mL, control the moisture content to 50%, perform 360 W ultrasonic extraction at room temperature for a certain time (20, 30, 40, 50, 60 min), centrifuge at 7500 r / min for 10 min, take the supernatant, obtain a polyphenol solution, and store it for later use.

[0172] Test Example 9

[0173] The concentration of polyphenols in different polyphenol solutions in Example 13 was determined by Folin phenol colorimetry. The results showed that the ultrasonic extraction time affected the polyphenol extraction rate. The extraction rate was the highest when the extraction time was 40 min, which was 8.61%, significantly higher than that of other time ( Fig.21 ).

[0174] Embodiment 14

[0175] A method for extracting polyphenols from pear fruit byproducts, comprising the following steps:

[0176] (1) Pretreatment: The pear byproducts were crushed with a wall-breaking machine for 2 min to obtain pear residue;

[0177] (2) Steam explosion: put the pear residue into the high-pressure tank of the steam explosion test bench, use saturated water vapor as the medium, the temperature of the saturated water vapor is 180°C to 230°C, the steam explosion pressure is 0.6 MPa, the pressure maintenance time is 2 min, quickly open the high-temperature and high-pressure valve to release the material into the storage tank, collect the pear residue in the storage tank, dry it to constant weight, and then use a wall breaking machine to crush the dried pear residue for 2 min to obtain pear residue powder for later use;

[0178] (3) Extraction of polyphenols: Accurately weigh 0.2 g of the pear residue powder obtained in step (2), add a low eutectic solvent consisting of choline chloride and ethanol (choline chloride and ethanol molar ratio of 1:2) to the pear residue powder at a solid-liquid ratio of 1 g:30 mL, control the moisture content to 50%, perform 360 W ultrasonic extraction at room temperature for 40 min, centrifuge at 7500 r / min for 10 min, take the supernatant, and obtain a polyphenol solution. The polyphenol concentration is determined by the Folin phenol colorimetric method and is 4.14±0.08 mg / mL.

[0179] Test Example 10

[0180] The DPPH free radical scavenging ability kit, ABTS free radical scavenging ability kit and total antioxidant ability kit were used to test the DPPH free radical scavenging ability, ABTS free radical scavenging ability and antioxidant ability of the polyphenol solution obtained in Example 14, respectively. The results are as follows: Fig. 22 shown.

[0181] according to Fig. 22 It can be seen that with the continuous increase of polyphenol concentration, the scavenging rate of ABTS free radicals is also increasing, indicating that the ability of polyphenols to scavenge ABTS free radicals is concentration-dependent, while the scavenging rate of DPPH free radicals and the total antioxidant capacity show a trend of first increasing and then decreasing. When the polyphenol concentration is 35 mg / mL, the scavenging effect on DPPH free radicals is the best, and its scavenging rate reaches 45.16%. The reason for the decline may be the degradation or conversion of free phenols in the system into other components. The scavenging rate of ABTS free radicals can reach up to 38.82%, and the total antioxidant capacity of polyphenols shows that the maximum reduction capacity of polyphenols to iron ions can reach 33.32 μmol / g.

[0182] From the above content, it can be seen that the method provided by the present invention has a simple process, can efficiently and quickly extract cellulose, pectin and polyphenols from pear fruit by-products, shorten the production cycle of pear fruit cellulose, pectin and polyphenols, and has high extraction efficiency, laying a foundation for the further development and utilization of pear residue cellulose, pectin and polyphenols.

[0183] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for extracting one or more of cellulose, pectin and polyphenols from pear fruit byproducts, characterized in that: The steps include: The pear fruit byproduct is subjected to steam explosion treatment and pulverization treatment in sequence to obtain pear residue powder; the steam explosion pressure of the steam explosion treatment is 0.3-2.0 MPa; Extracting the pear residue powder; the extraction includes one or more of cellulose extraction, pectin extraction and polyphenol extraction; The cellulose extraction step comprises: performing a first extraction on the pear residue powder using an alkaline solution, collecting the filter residue after reduced pressure filtration; bleaching the filter residue using hydrogen peroxide, collecting the filter residue after reduced pressure filtration, and drying to obtain pear crude cellulose; the pH value of the alkaline solution is 8-12. The pectin extraction step comprises: performing a second extraction on the pear residue powder using an acid solution and collecting the extract; performing alcohol precipitation on the extract and collecting the precipitate to obtain pear pectin. The polyphenol extraction step comprises: mixing the pear residue powder and a low eutectic solvent solution, ultrasonically extracting, and collecting the extract; the extract liquid contains pear fruit polyphenols; the low eutectic solvent solution comprises a hydrogen bond acceptor and a hydrogen bond donor; the hydrogen bond acceptor comprises choline chloride; the hydrogen bond donor comprises ethanol; and the molar ratio of choline chloride to ethanol is 1:(1-3).

2. The method according to claim 1, characterized in that The time of the steam explosion treatment is 1 to 5 minutes; the medium of the steam explosion treatment is saturated water vapor; the temperature of the saturated water vapor is 160 to 230°C.

3. The method according to claim 1, characterized in that The first extraction temperature is 75-90°C and the time is 2-4h; During the cellulose extraction, the mass volume ratio of the pear residue powder to the alkaline solution is 0.5-2 g:10-50 mL; the alkaline solution includes a sodium hydroxide solution, and the mass concentration of the sodium hydroxide solution is 7.5-15 wt %.

4. The method according to claim 1, characterized in that The bleaching treatment is performed 3 times, each time at a temperature of 75 to 90° C. and for 45 to 70 minutes; The mass concentration of the hydrogen peroxide is 1-2.5wt%.

5. The method according to any one of claims 1 to 4, characterized in that: After obtaining the pear fruit crude cellulose, the method further comprises: mixing the pear fruit crude cellulose with a purified solution, reacting at 90 to 120° C. for 20 to 60 minutes, collecting the filter residue after vacuum filtration, and drying to obtain purified pear fruit cellulose; The purified solution comprises 70-80wt.% acetic acid solution and 65-70wt.% nitric acid solution; the volume ratio of the acetic acid solution to the nitric acid solution is (1-10):(1-30).

6. The method according to claim 1, characterized in that The temperature of the second extraction is 75-85° C., and the time is 1.5-3 hours.

7. The method according to claim 1, characterized in that During the pectin extraction, the mass volume ratio of the pear residue powder to the acid solution is 0.5-2 g:10-50 mL; the acid solution includes a hydrochloric acid solution, and the concentration of the hydrochloric acid solution is 0.05-0.15 mol / L.

8. The method according to claim 1, characterized in that: The alcohol precipitation time is 10 to 15 hours; the alcohol precipitation uses anhydrous ethanol, and the volume ratio of the extract to anhydrous ethanol is 1: (1 to 5).

9. The method according to claim 1, characterized in that: During the polyphenol extraction, the mass volume ratio of the pear residue powder to the low eutectic solvent solution is 1g:(15-35)mL; the water content of the mixture of the pear fruit by-product powder and the low eutectic solvent solution is 20-60%.

10. The method according to claim 1, characterized in that The ultrasonic extraction time is 20 to 60 minutes, and the power is 300 to 700W.

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